The present invention is related to a calcium phosphate cement (CPC), and in particular to a method of shortening a working and setting time of a CPC paste.
As early as 1983 Brown and Chow have indicated that mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) powders in a diluted phosphate-containing solution led to the formation of hydroxyapatite (HA). According to this chemical reaction a calcium phosphate cement (CPC) was first developed and patented in 1986 [U.S. Pat. No. 4,612,053]. Thereafter, using this moldable CPC paste as bone substitute has brought a great deal of attention to the researchers and industry in this field and a variety of fabrication methods have been proposed.
One major advantage of CPC over calcium phosphate blocks or granules is that CPC paste can be molded to any desirable shape during operation. The paste hardens in-situ with HA as its main final constituent. By adjusting viscosity of the CPC paste, CPC paste is injectable using a surgical syringe that finds many applications for orthopedic, craniofacial and periodontal operations.
Yet there are still problems during practical application of CPC paste, at least including its prolong setting time and dispersion upon early contact with blood or aqueous media. Appropriate working/setting time is critical for surgical applications. Ideally a CPC paste should be applied when it is still workable and wound may be closed after the cement is set. Appropriate working times have been suggested not to be much longer than 8 min for orthopedic applications.
Different approaches were reported to shorten the setting time of CPC paste. Examples include increasing phosphate hardening solution concentration, using different hardening solutions, and mixing in calcium phosphate powders with such additives as HA, CaO, Na2O, P2O5, MgO, CaF2 and collagen. Nevertheless, these modifications are often accompanied with sacrifices in biocompatibility and/or mechanical strength.
A primary objective of the present invention is to provide a method of shortening a working and setting time of a CPC paste, which is accomplished by subjecting the CPC powder to a heat treatment without using additives or sacrificing its strength.